PCI: keystone: Use hwirq to get the MSI IRQ number offset

ks_pcie_msi_irq_handler() uses 'virq' to get the IRQ number offset.
This offset is used to get the correct MSI_IRQ_STATUS register
corresponding to the IRQ line that raised the interrupt.

There is no guarantee that 'virq' assigned for consecutive hardware
IRQ will be contiguous and this might get us an incorrect IRQ number
offset.

Fix it here by using 'hwirq' to get the IRQ number offset. Since we
don't store the 'virq' numbers of all the IRQ numbers, stop checking
if irq count is greater than MAX_MSI_HOST_IRQS and remove
MAX_MSI_HOST_IRQS.

Link: https://lkml.kernel.org/r/bb081d21-7c03-0357-4294-7e92d95d838c@arm.com


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>